Abstract: Using longitudinal wave method and self-made internal thread fixture, the common nut and self-locking nut were selected to calibrate the bolt respectively. Through different tightening strategies and calibration methods, the difference of characteristic curves of the bolt calibrated by common nut and self-locking nut were analyzed. The results show that different calibration characteristic curves can be obtained by using common nut and self-locking nut because the method was different. The locking torque of the self-locking nut made the bolt temperature rise, resulted in the increase of ultrasonic time difference, so the obtained calibration characteristic curve will move parallel to the right.